package tree;

/**
 * @author kaho
 * @since 2021/2/25
 */
public class _110_平衡二叉树 {


    /**
     * 给定一个二叉树，判断它是否是高度平衡的二叉树。
     * <p>
     * 本题中，一棵高度平衡二叉树定义为：
     * <p>
     * 一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过 1 。
     *
     * @param root
     * @return
     */
    public boolean isBalanced1(TreeNode root) {
        return dfs1(root) != -1;
    }

    private int dfs1(TreeNode treeNode) {
        if (treeNode == null) {
            return 0;
        }
        int left = dfs1(treeNode.left);
        if (left == -1) {
            return -1;
        }

        int right = dfs1(treeNode.right);
        if (right == -1) {
            return -1;
        }
        return Math.abs(right - left) < 2 ? Math.max(right, left) + 1 : -1;
    }

    public boolean isBalanced(TreeNode root) {

        return dfs(root) != -1;
    }

    private int dfs(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = dfs(root.left);
        if (left == -1) {
            return -1;
        }
        int right = dfs(root.right);
        if (right == -1) {
            return -1;
        }
        return Math.abs(right - left) < 2 ? Math.max(right, left) + 1 : -1;
    }
}
